Process and apparatus for dewaxing oil



Jan. 5,1937. H. F. FISHER ET AL PROCESS AND APPARATUS FOR DEWAXING OIL Filed Dec. 5, 1953 ww mm R mkb 1.

Lmxmmm QQ NQQ INVENTORS Blair 6?. Aldridge g5 Harmon FFzs/ver RED Al n N m T T A Patented Jan. 5, 193? pairs stares rA'reN'r FFlCE PROCESS AND APPARATUS FOR DEWAXING OIL poration of California Application December 5, 1933, Serial No. 700,996

7 Claims. (Cl. 204-24) The invention relates to the separation of wax from wax-bearing oil. The invention relates more particularly to the electrical separation of suspensions of precipitated wax from oil. This application is a continuation in part of application Serial No. 692,724 filed Oct. 9, 1933.

Crude oils from which lubricating oil is produced in many cases contains paramn or wax which is carried over and remains in the lubricating oil distillate fractions derived therefrom. If the temperature of these lubricating oil fractions containing wax or parafiin is sufiiciently lowered wax or paraffin is found to beglnto be precipitated from solution therein in the form of a colloidal suspension and if the, temperature is continued to be further lowered more wax is found to be precipitated until the resulting oil and wax mixture finally congeals to a semi-plastic or solid mass. Lubricating oil fractions containing relatively large quantities of wax have relatively high congealing temperatures while oils containing small quantities of wax have correspondingly lowered congealing temperatures. Thus it is apparent that the presence of wax limits the minimum temperature at which lubricating oils containing it can be used. The pour point of lubricating oil is that temperature 5 F. above the temperature at which the oil under certain specified conditions congeals or ceases to flow and it is apparent, according to the conditions stated hereinabove, that the presence of wax or parafiin in lubricating oil largely governs this characteristic of the oil. Therefore, in the production of lubricating oilv it is necessary to remove a large portion of the wax or parafiin in order to lower its pour point and thereby extend the lower ranges of temperatures at which it retains its fluidity and lubricating qualities.

The separation of wax or parafiin from lubricating oil may be accomplishedby a number of processes, two of the most common ones of which 7 are the cold settling process. and the cold pressing process.

In the cold settling process the wax-bearing oil may be first diluted with a quantity of a light hydrocarbon, such as liquid propane, naphtha,

' gasoline or kerosene. The diluted wax-bearing oil is slowly chilled by suitable refrigerating means for a period of 20to 50 hours until a lowered temperature is reached at which a substantial portion of wax is precipitated. The chilled oil and precipitate mixture is then allowed to stand for a period which may be as long asseveral weeks to allow the wax to settle to the bottom of the chilling tank.

In the cold pressing process the diluted waxdescribed cold settling process. Following this the resulting chilled mixture of precipitated. wax and oil is pumped through a filter press at a high pressure. The wax precipitate is collected upon the filter and the oil is removed as a pressed distillate relatively free from wax.

The objections to these processes are the neoessarily high cost of refrigeration for the long periods of time, the large outlay of chilling tanks and storage equipment required and the poor separation of oil andwax obtained. Moreover, amorphous and/or micro-crystalline wax has been found extremely diflicult if not impracticable to separate by the common filtration methods.

Objects of this invention, therefore, are to provide a method and apparatus for dewaxing oil wherein a substantial reduction of the length of time required for chilling the wax-bearing oil may be accomplished and wherein the attendant outlay of refrigerating equipment may be substantially reduced. Objects of this invention are, moreover, to provide a process and apparatus for dewaxing oil wherein the conventional, slow batch chilling method can be replaced by a meth od employing continuous rapid cooling such as those known as flash chilling and shock chilling which may include quick chilling resultant upon rapid evaporation of a freely volatile solvent under a quick pressure drop, or quick chilling in cooling coils shock chilling; wherein the costly chilling tanks can be eliminated, and wherein a complete and satisfactory separation of wax can be effected by subsequent conventional separation methods notwithstanding. Other objects of this invention are to provide a method and apparatus for electrically treating wax-bearing oil whereby filtration and/or settling operations are improved.

In general these objects are attained according to the invention through shock chilling the wax bearing oil containing the diluent to precipitate wax from'solution, subjecting the mixture of wax precipitate and oil thus formed to an intense electric field between electrodes adapted to be self-cleaning and subsequently separating the wax from the oil by settling and/or filtering the said electrically treated oil-precipitate mixture.

It has been found that the disadvantages inherent in the common methods of wax separation may be overcome by the process which will be described hereinafter. We have discovered that a wax precipitate in suspension in oil can be rendered more readily filtered or separated diluent and precipitated wax subjected to an intense electric field between self-cleaning or agglomerating type electrodes and the thus treated oil and precipitate mixture subsequently filtered. It has been found that the wax precipitate thus subjected to the electric treatment is agglomerated and/or otherwise modified in form and/or conditioned to be more readily filtered. It has also been discovered that an oil containing wax precipitate formed by shock chilling and subsequently electrically treated between self-cleaning electrodes, as hereinbefore described, can be filtered as readily as an oil containing wax precip itate which has been formed by the method of batch chilling alone. The effectiveness of the electrical treating in aiding filtration is particularly apparent in view of the fact that the same shock chilled wax-bearing oil is practically non-filterable prior to the said electric treatment. The wax-bearing oil containing precipitated. wax formed by shock chilling is of such a fine tex- -ture and possesses such characteristics that it renders ordinary filtration operations impractical by plugging the filter leaves. shock chilled oil, containing wax precipitate, upon being electrically treated, between selfcleaning electrodes is agglomerated and/or otherwise modified to a form which is filterable by ordinary methods.

It has also been discovered that by electrically treating the wax-bearing oil containing wax precipitate according to the hereinbefore described process, the wax is renderedmore readily settled, and in some cases the settling stage is employed subsequent to the electri. treating either alone or prior to filtering to separate-the wax precipitate from the oil. The diluent may be recovered by distillation subsequent to the separation of the wax from the solution according to the processes described hereinbefore.

Refrigeration of the wax-bearing oil-diluent solution may be accomplished either by means of external indirect heat exchange with a refrigerant prior to electrical treating or by direct cooling by means of evaporation of a normally gaseous liquid diluent from the wax-bearing oil solution prior to or during electrical treating. This refrigeration is preferably rapid but batch chilling over a relatively long period of time may also be employed in connection with electric treating with corresponding benefit in efiiciency of settling and/or filtration.

It has been found that ordinarily in an electric treater employing conventional type electrodes a large proportion of the precipitated wax is re moved from the wax-bearing oil-precipitate mixture in the form of a deposit or plate upon the electrodes between which the treating field is The same accuse means heretofore employed for removing deposited wax from the electrodes has been in the form of scrapers. We have discovered that the preferred method of operation in connection with settling and filtration is to employ an electric treater incorporating an electrode design which is self-cleaning in action. Thewell known phenomenon of electric windage" has been employed in the construction to maintain the electrodes free of wax. Any number of electrode structures may be employed to accomplish this but the preferable construction is that disclosed in patent application Serial No. 692,724.

The treater comprises in brief a gas tight shell in which is located a pair or plurality of electrodes adapted to contact the wax-bearing oil to be treated. Each pair of said electrodes is constructed to have a high effective area ratio with respect to one another. It has been found that where two oppositely charged electrodes of unequal area are placed in electrostatic relation to one another, that the fluid surrounding or in contact therewith is caused to flow in a rapidly moving stream from the electrode of smallest area to the electrode of largest area. This phenomena is taken advantage of in the construction of the present treater and as just stated hereinbefore the electrodes therein are constructed to have a high ratio of effective area.

The preferable construction, as illustrated in the drawing, comprises an outer cylindrical electrode and an inner electrode consisting of a series of conical elements axially positioned within the said cylindrical electrode. In operation currents of rapidly moving oil containing precipitated wax are found to flow downward and outward from the edges ofthe cones of the inner electrode and to impinge upon the inside surface of the outside cylindrical electrode. These currents are of suflicient intensity to wash or erode from this electrode surface any wax which tends to be deposited thereon. The wax particles of the wax precipitate in the chilled oil are in a majority of cases negatively charged and, therefore, tend to be deposited on the positively charged electrode only. Therefore, by maintaining the outside cylindrical electrode positively charged the tendency of wax deposition is confined to this electrode and no special means is, therefore, necessary to maintain the inner or negatively charged electrode free from wax. In some cases where the charges on the precipitated wax particles are found to be of different polarity, the polarity of the electrodes may obviously be reversed as required to cause the deposition of the wax to tend to take place on the electrode from which it is being continuously removed by the windage currents.

The invention broadly stated comprises a method of treating wax-bearing oil with an electric field or current between self-cleaning or agglomerating type of electrodes to aid separation of wax therefrom.

The invention more specifically stated com- 2,067,162 prises a process and apparatus for treating waxbearing oil and/or wax-bearing 011 containing precipitated wax in suspension wherein the said wax-bearing oil and/or the wax-bearing oil containing precipitated wax in suspension is subjected' to an electric field or current between selfcleaning or agglomerating type electrodes to ag-.

glomerate or modify the precipitated wax, and" wherein the said precipitated waxthus treated is subsequently separated from the oil by filtration. The invention also comprises a process for treating wax-bearing oil and/or wax-bearing. oil containing precipitated wax in suspension wherein the said mixtures are subjected to an electric field or current between self-cleaning or agglomerating type electrodes to agglomerate and/or otherwise modify the wax precipitate to aid subsequent separation by settling methods. The invention also resides in a process for'dewaxing oil wherein shock chilled" wax-bearing oil is subjected to an electric field between self-cleaning or agglomerating type electrodes to render the wax precipitate thus formed readily separable by filtration or settling methods.

Other objects and advantages and features of the invention will be evident hereinafter.

The accompanying drawing illustrates one embodiment of the invention in which I is a storage tank to contain a supply of wax-bearing oil to be treated. Numeral I indicates a pressure storage tank for containing a diluent, such as liquid propane to be added to the wax-bearing oil. An interchanger or refrigerator for. indirectly chilling the wax-bearing oil-diluent solution is illustrated at 20. A chilling tank 32 is provided in which the wax-bearing oil-diluent solution may beallowed ,to accumulate and in which the normally gaseous diluent, when such a diluent is employed, may be allowed to evaporate at reduced pressure to accomplish'refrigeration of the said wax-bearing oil. The treatercomprises a gas tight cylinder 40 having a spherical head 4| and a conical bot tom 42 and containing a pair of electrodes 43 and 44. The electrode system comprises an outer:

cylindrical electrode 43 and an inner axially positioned electrode consisting of a series of superimposed hollow sheet metal cones 45 supported by rod 46 and lead-in insulator bushing 41. These cones '45 thus ofier thin edges or points in opposition to the surfaceof the cylindrical electrode 43, which structure is conducive to the formation of electric windage currents between these cone edges and said surface ofthe cylinder 43 when the electrodes are charged to a high potential difference. A wax pump50 is provided at the apex of the inverted conical bottom 42 by means of which settlings may be ejected through line A high electric potential ismaintained between the electrodes 43 and 44 by means of a high potential generator 55 making .connection to the inner electrode 44 through. electrical conductor 56, lead-in insulator 41 and rod 46 and completing the circuit to the outer electrode 43 through the electrical conductor 51 and the metallic treater body.

A settling chamber is provided in connection with the electric treater into which the electrically treated oil containing precipitated wax may be introduced for settling and separating the wax. Wax pump H is provided at the bottom thereof by. means of which settlings may be ejected through line 12.

containing precipitated wax may be filtered to separate the wax from the oil. Wax is periodically removed from the filter through line 8|. A pump 64 serves to supply the necessary oil pressure to the filter 80.

A still 90 is provided to receive the oil filtrate or decantate containing solvent. Solvent is evaporated and separated from the oil in still 9|l'by means of heat supplied through heatingcoil 9|. A cooler 92 is provided on the bottoms outlet from the still 80 and a storage tank 95 into which is delivered the dewaxed oil from the bottoms of the still. Acooler I00 isprovided in the vapor return line from the still and chiller. A pump 99 is provided for compressing vapors prior to cooling and a pump 0| is provided for returning condensate to the diluent storage tank.

The operation is as follows: Wax-bearing oil at a temperature above that at which wax is precipitated from solution is pumped from tank Ill by means of pump I through line and valve Hi to mixer 4 where it meets a stream of solvent flowing from storage tank through line I2 and valve l3. The ratio of wax-bearing oil to diluent meeting and dissolving in one another at mixer I4 is governed by regulation of the valves l3 and IS. The solution of wax bearing oil and solvent flows from mixer |4 through the refrigerator where it passes in indirect heat exchange with a suitable refrigerant to reduce its temperature to a point where wax precipitate forms. The thus cooled wax-bearing oil containing wax precipitate after passing through refrigerator 20 is withdrawn and may-flow through lines 2| and 24, valve 25, lines 26 and 21, pump 28 and inlet 23 to the electric treater.

In some cases instead of chilling the wax bearing oil by indirect heat exchange with a refrigerant in a refrigerator, as illustrated here at 20,

the wax-bearing oil is allowed to flow through the refrigerator 20 whichis rendered inoperative exhausts vapors formed in the chilling tank 32' through vapor outlet 33, valve 34 and line 35. Regulation of the pressure on the vapors iii the chilling tank 32 is accomplished by adjustment of valves 34 and 98. C I l The wax-bearing oil-diluent solution'containing precipitated wax after refrigeration in chilling tank 32, as hereinabove described, is with drawn from thebottom thereof through valve 30 and lines 3| and 21 and forced by means of pump 28 through inlet 29 into the electric treater.

The chilled wax-bearing oil after entering the electric treater through inlet 29, passes downward therein between the electrodes 43 and 44 where it is subjected to an intense electric field.

After being elec rically treated between the electrodes 43. and 44 the wax-bearing oil flows out of the electrode system and into the space 48 inside of the treater shell 40 surrounding the electrode system. A small portion of the wax precipitate in the thus electrically treated waxbearing oil may settle to the bottom of the treater and any such settlings, when sufilcient quantity has accumulated, are withdrawn and ejected through line 5| by means of wax pump 50.

The oil-diluent solution containing most of the electrically treated precipitated, wax moves upward in the space 48 in the treater and is withdrawn through outlet 58 near the top thereof.

.A pressure is maintained in the electric treater by means of pump 28 sufficient to prevent ebullition therein of the oil-diluent solution which would be detrimental to the electric treating and settling operations.

The oil-diluent solution containing electrically treated precipitated wax which is withdrawn fromthe treater through outlet 58 may pass through valve 59, lines 62 and 63 and be forced by means of pump 64 through line 65, valve 66 and connection 61 through the filter press 80. The oil-diluent solution from which the electrically treated wax precipitate has been removed in filter press 80 continues in flow through the filter outlet connection 82 and inlet connection 83 into The diluent vapors stripped from the dewaxed oil fractions in still 90 are withdrawn from the top thereof through vapor: line 96 and after passing through valve 98 are compressed along with other diluent vapors issuing from the chilling tank 32 through lines 35 are compressed by means of compressor 99, cooled in .cooler I00 I and the resultant condensate returned by means of pump IBI to the diluent storage tank H. In case the diluent employed in the process is nor-' mally liquid the vapors thereof issuing from the still may be condensed in the cooler I00 without previous compression and the condensate returned to the diluent storage tank II by means ofpump l0l. When such a non-volatile normally liquid diluent is employed refrigeration of the solution will obviously be accomplished entirely by indirect heat exchange with a refrigerant. as in refrigerator 20.

In some cases it may be desirable to separate the .wax fromthe electrically treated oil-diluent solution containing precipitated wax by settling and this may be accomplished by allowing the said treated material withdrawn from the electric treater through line 58 to flow through valve 60 and inlet 6| into the settling chamber 10, in thiscase valve 59 is closed. The wax removed from the oil inthe settling tank 10 by means of settling, is ejected from the bottom thereof through line 12 by means of wax pump I l. The oil-diluent solution from'which the wax has thus been re! moved by settling is withdrawn from the top of settling tank 10 through outlet 13, valve 14 and line 63 to pump 64 by which it isforced through line 65 and filter by-pass lines "84 and 85 and valve 86 into the still 90 through inlet 83. When operating in this manner without filtration, valve 66 is closed. t

It is sometimes found advantageous to combine the hereinbefore described operations of settling and filtering wherein a portion of the wax 'is removed by settling in settling tank 10 and the remaining wax removed by filtration in filter .80. When it is desired to so operate the oil-diluent solution withdrawn from the settling tank 10 is also passed through the filter 80 before reaching the still 90. When operating in this manner the filter by-pass valve 86 is closed and the valve 66 opened.

A high potential electric field is maintained in the treating zone between the cones 45 of the electrode 44 and the surface of the cylindrical electrode 43 by means of a suitable high voltage source, such as generator 55. The circuit through the generator 55 from the electrodes 43 and 44 is, completed through rod 46, lead-in insulator bushing 47, conductors 56 and 51 and the metallic treater body.

The electric potential supply 55 may be adapted to supply either direct current, interrupted unidirectional current 'or alternating current. In general, it has been found advantageous to maintain a unidirectional potential between the electrodes either interrupted or continuous with the positive tions.

The cooling rates of the contents of the chilling tank 32 may be governed by the rate of evacuation or withdrawal of vapors therefrom through valve 34 to obtain a range of cooling conditions varying from batch chilling to flash chilling. For example, if it is desired to batch chill or slowly chill the oil or oil-diluent solution to be electrically treated, the pressure upon the contents of the chilling tank is slowly reduced over the desired period oftime and at the desired rate until the minimum desired temperature is attained, at which point the said contents are withdrawn and allowed to pass through the. electric treater. On the other hand, if it is desired to quickly cool or shock chill, the oil-diluent solution is allowed to continuously flash through valve 23 into the tank 32 which is maintained at reduced pressure. Cooling rates may also be governed over a wide range by manipulation of the interchanger 20.

Diluents which may be used for refrigeration are liquid propane, butane and methylchloride. It has also been found possible to cool the contents of the chiller and the electric treater chambers by mixtures therein of liquid sulphur dioxide or ammonia; Other diluents which may be em ployed to prevent congealing of the chilled waxbearlng oil are naphtha, gasoline, liquid propane, acetone and benzol, methyl chloride, halogenated hydrocarbons, such as monochloro difiuoro methane, dichlorodifiuoro methane, dichlorethylene, trichlorethylene, ethers or mixtures of ethers and alcohols and gas oil or other heavy oils including dewaxed lubricating oil fractions.

The self-cleaning or agglomerating type of electrode system as described and illustrated herein has been found to possess the ability, when charged to a high potential difference, to agglomerate or modify the form of the wax precipitate formed in wax-bearing oils, in such a manner that subsequent treatment by filtration to separate wax is greatly improved in effectiveness and eficiency. This may be due to a tendency for the wax precipitate particles to be deposited and to accumulate in relatively large concretions or flocks upon the electrode of opposite polarity, before being detached by the force of the electric windage current in the liquid or it may be due to subjection of the precipitate tothe extremely high potential gradients which are formed between electrodes, such as those illustrated herein, where vby flashing it into a chilling drum at reduced pressure. This flash chilled solution was fed to the electric treater at a' rate such that the waxbearing liquid solution remained in the electric treating field for a period of approximately one half hour. An average potential gradient of 75,000 volts per inch was maintained through the material being treated.

The thus electrically treated wax-bearing oil was run through a filter at'a constant pressure of 50 pounds per square inch and filtration rates varying from 0.3 to 0.5 gallon per square foot per hour obtained over a number of experimental runs.

The same flash chilled wax-bearing solution without electrical treatment was run through the same filter and filtration rates varying from 0.07 to 0.19 gallon per square foot per hour were obtained.

It is apparent from these results that average filtration rates for the electrically treated solution under the same chilling and filtering conditions was three times as great as that for the untreated flash chilled solution. Pour points of the filtrates obtained throughout the tests varied from to 10 F.

- The process and apparatus is not to be limited to the specific structure, nor to the treatment of pair of oppositely charged electrodes, whereby wax particles agglomerate and certain of said wax particlestend to migrate and deposit upon an electrode of one polarity, establishing an electric windage from the other electrode of opposite polarity toward the surface of said first named electrode of sufiicient intensity to prevent permanent deposition of wax particles thereon.

2. A process for dewaxing oils which comprises passing a stream of wax-bearing oil between a pair of oppositely-charged electrodes whereby wax particles agglomerate and tend to migrate and deposit upon an electrode of one polarity, maintaining an electric potential upon the other electrode of opposite polarity sufficiently high to establish a sufficient fluid disturbance in said stream of wax-bearing oil in the direction of the surface of said first named electrode to prevent permanent deposition of wax particles thereon.

3. A process for dewaxing oils which comprises chilling said oil to precipitate wax therein, passing a stream of said wax and oil between spaced oppositely charged electrodes whereby wax particles agglomerate and tend to migrate and to deposit upon electrodes of one polarity, maintaining an electric potential upon electrodes of opposite polarity to'establish an electrical windage circulatory current in said oil in the direction of said first named electrodes whereby wax particles accumulating upon said electrodes are removed by the erosive action of said circulatory currents, and withdrawing agglomerated wax and oil from said electric field in a direction substantially concurrent to said electrical windage.

4. A process for dewaxing oil which comprises passing a mixture of oil and wax between an elec-' trode of one polarity having a relatively large surface and an electrode of opposite polarity having a relatively small surface, inducing an electric fieldbetween said electrodes whereby wax particles agglomerate and tend to deposit upon said electrode of relatively large surface, establishing an electric windage adjacent the surface of said electrode of relatively small surface in the direction of said electrode of relatively large surface of suflicient intensity to dislodge wax depositing on said last named electrode.

5. A process for dewaxing oils which comprises passing a stream of wax-bearing oil between a pair of oppositely charged electrodes whereby wax particles agglomerate and certain of said wax particles tend to migrate and deposit upon an electrode of one polarity, establishing an electric windage from the other electrode of opposite polarity toward the surface of said first named electrode of sufiicient intensity to prevent permanent deposition of wax particles thereon and filtering the thus agglomerated wax from the oil.

6. A process for dewaxing oils which comprises chilling said oil to precipitatewax therein, passing a stream of said wax and oil between spaced oppositely charged electrodes whereby wax particles agglomerate and tend to migrate and to deposit upon electrodes of one polarity, maintaining an electric potential upon electrodes of opposite polarity to establish an electrical windage circulatory current in said oil in the direction of said first named electrodes whereby wax particles accumulating upon said electrodes are removed by errosive action of said circulatory currents,

and filtering the thus agglomerated wax from the oil.

7. A process for dewaxing oil which comprises passing a mixture of oil and wax between an electrode of one polarity having a relatively large surface and an electrode of opposite polarity having a relatively small surface, inducing an electric field between said electrodes whereby wax particles agglomerate and tend todeposit upon said electrode of relatively large surface, establishing an electric windage adjacent the surface of said electrode of relatively small surface in the direction of said electrode of relatively large surface of sufiicient intensity to dislodge wax depositing on said last named-electrode and filtering the thus agglomerated wax from the oil.

BLAIR G. ALDRHJGE. HARMON F; FISHER. 

